The present invention relates to an arrangement and a method for controlling a control valve for a diesel injection system.
A control valve arrangement and method for controlling the same are disclosed in U.S. Pat. No. 5,640,987. Diesel engines with direct injection have the highest thermodynamic efficiency of all internal combustion engines. In terms of fuel injection, different technologies are in use for different engines. Particularly in the commercial vehicle sector, systems with pressure transmission for generating higher pressures have become standard practice. An example of a fuel injector with pressure transmission is described in U.S. Pat. No. 5,460,329 (Sturman). Here, the fuel is fed to a pressure booster in the injector via an electromagnetic control valve which is embodied as a slide valve. The fuel is placed under high pressure by the pressure booster at fixed times or crank angles by means of the electromagnetic actuation of the control valve. The fuel which is placed under high pressure then causes the valve needle of the injector to lift off from its seat and clear the path for the fuel to be injected from the injection nozzle of the injector into the combustion space of the diesel engine.
The control valve has in each case one electromagnet in the region of each of the two ends of the valve slide in order to be able to be switched back and forward without elastic restoring elements being necessary. However, in order to keep the control valve in a defined position, current must continue to be supplied to one of the two magnets even after the desired position has already been reached.
For this reason, Sturman developed the electromagnetic control valve in the way described in U.S. Pat. No. 5,640,987. In this refinement, the valve slide and the housing of the control valve are composed of suitable magnetic materials so that even without current the valve slide remains in the respective limit position owing to the hysteresis of the magnetic material of the slide. For switching over, all that is necessary is for current to be briefly supplied to one of the two solenoids. After the switching over has occurred the current can then be switched off. This type of control valve is referred to as a digital valve owing to its bistable behavior. The valve can be embodied as a 2-way, 3-way or 4-way valve.
Such a control valve is also described in U.S. Pat. No. 5,720,261. The feeding of current to the actuated solenoid is interrupted as soon as the control valve is in a limit position. To do this, the non-actuated solenoid is used as a sensor which detects the end of the movement of the control valve.
However, unavoidable fabrication tolerances and thus the inevitably different pairing interplay between the valve slide and the valve housing at the control valves of the individual injectors of an injection system for a multicylinder engine and differences in the masses of the valves and difficulties in the valve setting bring about a different injection behavior of the individual injectors at the different cylinders of the engine, and as a consequence non-uniform behavior of the engine, in particular through running problems.
The object of the present invention is to configure the control valve in such a way that the wide-ranging variation of the injectors in terms of injection behavior is reduced and the engine runs in a better and more uniform way. The object of the present invention is achieved according to the invention in that while current is supplied to one of the two solenoids of the control valve in order to generate a magnetic force, the other solenoid of the respective control valve is switched as a sensor for a movement of the valve slide. Because the valve slide is composed of a magnetic material, the magnetic properties and the hysteresis properties of this material permit a movement of the valve slide while the control current is acting, and even after it has been switched off, induces a current or a voltage for the one solenoid in the sensor. The information which is obtained in this way during a number of operating cycles about the characteristic response behavior of the control valve when actuation occurs can be processed within the scope of an intelligent control in such a way that the injection behavior of the respective injector is improved to the effect that deviations from the individual setpoint values of the injection parameters are reduced. For example, a relatively long dead time between the start of the energization of the solenoid and the start of the movement of the valve slide in the case of a control valve, or generally a delayed switching behavior as a result of an earlier start of the energization or a different voltage supply can be compensated.
Even if the two electromagnets are connected in parallel during operation in order to increase the speed, it is possible to determine, within a short time and from a small number of cycles of the switching operation with just one activated magnet, the characteristic behavior of the valve with a sufficient precision to approximate the actual behavior to the desired behavior by means of appropriate measures.
The arrangement and method according to the present invention have the advantage that no additional components are required on the injector such as a stroke sensor and the like. The method according to the present invention can, for example, be carried out relatively easily by means of suitable software in the existing electronic engine controller. The application as originally filed in German is incorporated herein by reference.